The invention relates to a microtome having a handwheel for driving a specimen holder.
Sliding microtomes may be provided with a drive handwheel on one of the sides of an oblong box-shaped housing, and with a specimen holder which executes a horizontal reciprocating movement inside the microtome housing when the handwheel is operated, that is to say, when it is rotated in one or the other of the two directions. The specimen holder moves relative to a cutting knife which is fastened to the housing. In such microtomes, the specimen holder commonly executes a cutting movement beneath the cutting knife when the handwheel, which is normally installed on the right-hand side of the microtome housing, is rotated in a clockwise direction. During this cutting movement, a thin section of a specimen held by the specimen holder is produced.
When the handwheel is rotated anticlockwise, the specimen holder executes a resetting movement, during which it is automatically displaced through a small distance, away from the cutting knife, so that the cutting knife does not scrape against the cut surface of the thin section specimen during the resetting movement, which would damage the cut surface or, possibly, result in wear of the cutting edge.
However, in known microtomes of this kind, the cutting movement and the resetting movement are both executed at the same speed. In order to carry out an accurate cut, it sometimes becomes necessary, in the case of hard specimens, to rotate the handwheel more slowly during the cutting movement than during the resetting movement. The resetting movement should be executed more rapidly in order to increase the efficiency of the thin section preparation work. However, in the case of known microtomes, the slow rotation of the handwheel during the cutting movement requires that the operators should possess adequate experience, and accordingly the quality of thin sections produced by means of a microtome of this type is also dependent on the experience of the operator.